The invention concerns a metallurgical vessel having a tapping apparatus for the controlled slag-free withdrawal of liquid metal. The invention also relates to a process using such a tapping apparatus.
WO 86/04980 discloses an apparatus and a process for transferring a predetermined amount of liquid metal from a receiving container containing a molten metal bath, by means of a discharge pipe with a refractory lining, using the principle of a liquid siphon. The discharge pipe is in the form of an inverted U or V with two downwardly facing legs, of which the first has an inlet opening and the second has an outlet opening for the liquid metal, which can be gas-tightly closed by a closure device. Provided in the upper region of the discharge pipe is a pipe connection which can be connected to a vacuum device and which has a refractory lining and which can be selectively connected to the vacuum device by way of a first valve or communicated with the free atmosphere by way of a second valve. For the purposes of transferring a predetermined amount of liquid metal from the vessel containing a molten metal bath, in particular a smelting furnace vessel, the first leg of the discharge pipe whose second leg is gas-tightly closed by the closure device is immersed in the molten metal bath through a closable opening in the wall of the upper vessel portion formed by water-cooled elements, the second valve which acts as a ventilation valve is closed and the first valve is opened to communicate the discharge pipe with the vacuum device. The vacuum suction effect of the vacuum device causes the molten metal to be lifted in the first leg and it passes into the second leg over an overflow edge in the connecting region of the two legs. When the second leg is filled, the closure device of the second leg is opened and the liquid metal is transferred on the basis of the principle of the liquid siphon into the receiving container, preferably a ladle. By closure of the first valve which makes the communication with the vacuum device and opening of the second valve which acts as a ventilation valve, the flow through the discharge duct can be interrupted so that controlled, slag-free withdrawal of the molten metal is possible. In order to prevent slag from passing into the discharge pipe when the first leg is immersed in the molten metal bath through a layer of slag, the inlet opening, prior to being immersed in the molten metal bath, is closed by a plate which, after immersion, melts and opens the inlet opening. To protect the closure plate member of the closure device, prior to tapping of the furnace vessel granular refractory material is introduced into the second leg which moreover has a constriction in the lower region.
DE-C 605 701 discloses a siphon for emptying thermal baths, in which an ejector nozzle is installed in the suction pipe which is surrounded by a heating casing. The ejector nozzle, together with the suction pipe, is heated. The ejector nozzle produces a reduced pressure with which the procedure for the controlled withdrawal of the liquid from the vessel is initiated.
In the known processes and apparatuses for the withdrawal of liquid metal using the principle of a liquid siphon, a leg of the discharge pipe which is in the form of an inverted U or V is immersed in the molten metal bath. The upper direction-changing region of the discharge pipe is disposed above the maximum height of the molten metal surface. Therefore, to initiate the tapping procedure, the molten metal must be raised by more than the difference in height between the direction-changing region and the surface of the molten metal. That makes a vacuum device necessary to initiate the tapping procedure.
The object of the present invention, in a metallurgical vessel having a tapping apparatus, irrespective of the size of the vessel, is to permit reliable controlled slag-free withdrawal of liquid metal. The invention aims to set forth various modifications in the tapping apparatus in which it is possible to initiate the tapping procedure without a reduced pressure, so that there is no need for a vacuum device. Finally the invention also seeks to provide a process for the controlled, slag-free withdrawal of liquid metal from a metallurgical vessel, using an apparatus of that kind.
Advantageous configurations of the tapping apparatus, in accordance with the invention, are to be found in the embodiments described herein. Advantageous configurations of the process, in accordance with the invention, are also to be found in the embodiments described herein.
In the case of the present invention the discharge duct is integrated with one leg into the wall of the vessel and the height of the overflow edge in the connecting region of the two legs of the discharge duct is established in such a way that it is possible to eliminate the vacuum device for initiating the tapping operation. In that respect, by pressure equalisation between the free atmosphere and the connecting region of the two legs, preferably by way of a ventilation valve or by actuation of the closure device it is possible for the tapping operation to be rapidly broken off at any time, so that it is possible to ensure that, when the liquid metal is withdrawn, no slag is also entrained from the layer of slag which floats on the molten metal.